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  • ppm and density

    I'm working on a problem that starts out saying "An 11.0 ppm solution (density 1.3 g/mL)..."

    Wouldn't 11 ppm (mg/L) be entirely different than 1.3 g/mL? I'm really confused by this, am I missing something obvious?

    Any help is appreciated!

    Jess

  • #2
    Re: ppm and density

    Originally posted by Jess2007
    I'm working on a problem that starts out saying "An 11.0 ppm solution (density 1.3 g/mL)..."

    Wouldn't 11 ppm (mg/L) be entirely different than 1.3 g/mL? I'm really confused by this, am I missing something obvious?

    Any help is appreciated!

    Jess
    Well, every solution is 1 million ppm total, here 11 ppm of something interesting, and 999989 parts of something boring. The total mixture has a density of 1.3 g/mL.

    Whatever the 11 ppm component is, its concentration is 11 ppm * 1.3 g/mL = 14.3 g/mL.

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    • #3
      Re: ppm and density

      Thanks so much for the quick reply. The problem makes much more sense now.

      - Jess

      Comment


      • #4
        Re: ppm and density

        Originally posted by JohnS
        Well, every solution is 1 million ppm total, here 11 ppm of something interesting, and 999989 parts of something boring. The total mixture has a density of 1.3 g/mL.

        Whatever the 11 ppm component is, its concentration is 11 ppm * 1.3 g/mL = 14.3 g/mL.

        Something got confused here, she has already said that the concentration is 11ppm (mg/L), so the concentration is still 11g/mL.

        You can have a solution of any density, that still has a concentration of 11ppm (mg/L). If this is stated, then the density is immaterial.

        Hope this helps.

        Comment


        • #5
          Re: ppm and density

          Originally posted by Mrs X
          Something got confused here, she has already said that the concentration is 11ppm (mg/L), so the concentration is still 11g/mL.

          You can have a solution of any density, that still has a concentration of 11ppm (mg/L). If this is stated, then the density is immaterial.

          Hope this helps.
          Perhaps, but I don't agree that is the best interpretation of the given data. Ppm is ALWAYS confusing (hence deprecated) as to what basis it is stated on. However, the density of the solution is given, 1.3 g/mL. It does NOT state that the ppm is given as mass/volume. While I acknowledge the equivalence of 1 kg = 1 L for dilute aqueous solutions, ppm should have equivalent units in the numerator and denominator. I assumed it was stated on mass/mass basis, and a density of 1.3 certainly requires density correction (I would argue for density correction of seawater at 1.025)

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          • #6
            Re: ppm and density

            Originally posted by JohnS
            Perhaps, but I don't agree that is the best interpretation of the given data. Ppm is ALWAYS confusing (hence deprecated) as to what basis it is stated on. However, the density of the solution is given, 1.3 g/mL. It does NOT state that the ppm is given as mass/volume. While I acknowledge the equivalence of 1 kg = 1 L for dilute aqueous solutions, ppm should have equivalent units in the numerator and denominator. I assumed it was stated on mass/mass basis, and a density of 1.3 certainly requires density correction (I would argue for density correction of seawater at 1.025)
            Have a read through of the original question again.

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            • #7
              Re: ppm and density

              OK, here we go:

              I'm working on a problem that starts out saying "An 11.0 ppm solution (density 1.3 g/mL)..."
              That's all we're given.

              Ppm is always ambiguous so it becomes "what would you like it to mean." (out of the three or four possible choices). However, I read as a mass/mass ppm statement (11 g/g) of a solution having a density of 1.3 g/mL.

              You read it differently, as 11 g/mL. Neither of us have much basis as we don't even have the whole problem. It could equally well be 11 L/L or 11 mol/mol, although we would probably agree those are unlikely for a liquid.

              In any case, a ratio of explicit units 10^6 apart are far better than slapping the letters "ppm" on it.

              Comment


              • #8
                Re: ppm and density

                Originally posted by JohnS
                OK, here we go:



                That's all we're given.

                Ppm is always ambiguous so it becomes "what would you like it to mean." (out of the three or four possible choices). However, I read as a mass/mass ppm statement (11 g/g) of a solution having a density of 1.3 g/mL.

                You read it differently, as 11 g/mL. Neither of us have much basis as we don't even have the whole problem. It could equally well be 11 L/L or 11 mol/mol, although we would probably agree those are unlikely for a liquid.

                In any case, a ratio of explicit units 10^6 apart are far better than slapping the letters "ppm" on it.
                The next line says 11ppm (mg/L). You have made it quite clear you don't like the use of "ppm", but it is widely used in chemistry to mean mg/L, regardless of your opinion. There is very little point in trying to change that via this forum. It causes confusion and misunderstanding, and does not help people.

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                • #9
                  Re: ppm and density

                  Hi. i am really confused on how to compute the mass given the concentration: 1000 ppm. and the volume - 1 liter. please help.

                  Comment


                  • #10
                    Hi,

                    I hope the below helps. Please refer to the below examples that were done based on solids.

                    PPMW = weight of solute / weight of solution (i.e. weight of solute + weight of liquids) * 106

                    Example:
                    80 mg in 10 Litres of solution
                    Density of the solution (1,051 kg/m^3) (Note: weight of solids + weight of liquids)

                    Calculation
                    PPMW = ((80 / 1,000,000) / ((10 / 1,000) * 1,051)) * 10^6 = 7.61
                    PPMW = (80 mg into kg) / ((10L in m^3) * solution density of 1,051 kg/m^3) * 1,000,000 = 7.61

                    Comment


                    • #11
                      PPMV = volume of solute / volume of solution (i.e. volume of solute + volume of liquids) * 10^6

                      Example:
                      81.62 mg in 10 Litres of solution
                      Density of solids (2,650 kg/m^3) (Note: volume of solids + volume of liquids)

                      Calculation
                      PPMV = (((81.62 / 1,000,000) / 2,650) / (((81.62 / 1,000,000)/2,650) + 0.01) * 10^6 = 3.08
                      PPMV = ((81.62 mg of solids converted in kg) / (Density of Solids 2,650 kg/m^3)) / (((81.62 mg of solids converted in kg) / (Density of Solids 2,650 kg/m^3)) + 10 L of liquids converted in m^3) * 10^6 = 3.08
                      PPMV = Volume of solids in m^3 / (Volume of solids in m^3 + Volume of liquids in m^3) * 10^6= 3.08

                      Comment


                      • #12
                        PPM = weight of solute / weight of solution * 10^6
                        This calculation is assuming the solution to be water, which 1 ppm is approximately equal to 1 mg/L of contaminant in water.

                        Example:
                        6 mg/L in 1 Litre of water
                        1L of water = 1kg

                        Calculation
                        PPM = ((6 / 1,000,000) / (1) * 10^6 = 6
                        PPM = (6mg converted into kg) / ((1L converted in kg) * 1,000,000 = 6

                        Let me know your thoughts.

                        Kind regards.

                        Comment

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